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Medical CO2 Build up in Bedroom?

  1. Apr 28, 2010 #1
    Just curious how long an adult person can stay in an average small (W=2.5metre x L=3.5m x H=2.4m) bedroom with the door & window shut before CO2 levels become dangerous?

    And what about a small room like ~ w1.4m x L1.4m x h1.6m? I assume the small size would make a dramatic difference?

    Because co2 is heavier would most of it sink to the floor?
    any input is appreciated thanks.
     
  2. jcsd
  3. Apr 28, 2010 #2

    mgb_phys

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    Normal breathing is around 6l/min and the air you breath out is about 5% CO2
    So a room W=2.5metre x L=3.5m x H=2.4m = 21m^3 = 21,000l

    So you would have breathed all the air in the room in 21000/6 min = 3500min = 60hours
    At that point the air would be 5% CO2 which is toxic but not immediately fatal - you wouldn't be very well though!
     
  4. Apr 28, 2010 #3
    cool, thanks for the reply.

    Very interesting
     
  5. Apr 28, 2010 #4

    russ_watters

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    That assumes the room us completely sealed, which it isn't. The reality is the concentration will never become problematic.
     
  6. Apr 28, 2010 #5
    Carbon dioxide is not toxic, it is carbon monoxide which is.

    The problem with carbon dioxide is if it replaces the oxygen in the air, when its concentration increases.
     
  7. Apr 28, 2010 #6
    It's less toxic than carbon monoxide, but still toxic.
     
  8. Apr 28, 2010 #7

    mheslep

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    I assumed the same thing, but apparently not true. If CO2 reaches 1.5%, or ~40X normal, it becomes toxic, even if the O2 level remains sufficient to support respiration.
    http://www.co2science.org//articles/V5/N48/EDIT.php
     
    Last edited: Apr 28, 2010
  9. Apr 28, 2010 #8
    I'd be interested in your references and reasoning, if available?


    Mheslep
    I didn't see any figures to support the statement that if you increase CO2 to 1.5% or beyond in the presence of unchanged O2 percentage it was toxic, perhaps I was too quick reading it?
     
    Last edited: Apr 28, 2010
  10. Apr 28, 2010 #9

    mheslep

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    Also states the harm occurs via acidosis in the blood.
     
  11. Apr 28, 2010 #10
    But it doesn't state that the oxygen concentration is unchanged.

    There are lots of references to show what happens if CO2 replaces oxygen, which is normally what happens, but I haven't seen any that state what happens if it replaces say nitrogen. Wikipedia is particularly gory.

    My copy of Chemistry for the Medical Sciences devotes nearly a chapter to the biochemistry of CO2, but doesn't help here either, so I would appreciate reference to any study that covers increased CO2 without oxygen replacement.
     
    Last edited: Apr 28, 2010
  12. Apr 28, 2010 #11

    russ_watters

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    That's because it is irrelevant whether the oxygen content has changed or not.

    Humans go without oxygen bottles at the Everest base camp, where there is half as much oxygen as at sea level....so equivalent to 10.5% oxygen concentration at sea level. But if you were to replace half the oxygen with CO2 at sea level, leaving 10.5% of each, you'd die because it isn't the displacement of oxygen, it is the toxicity of CO2 that kills you.
    It is due to misunderstandings, but the first link for a google for "carbon dioxide poison" gives this link, which has a detailed description of the misconception itself:
    http://www.inspectapedia.com/hazmat/CO2gashaz.htm

    Here's an interesting one:
    http://www.ecureme.com/emyhealth/data/Hypercapnia.asp

    Basically, it is saying that if you have a reduced lung capacity, it gets tough to strike a balance between getting enough oxygen and getting rid of enough CO2. If your lung capacity increases, your ability to get rid of CO2 decreases at the same time as the ability to take in oxygen decreases. But if you give pure oxygen, breathing slows and you can no longer get rid of CO2 fast enough, despite not breathing any in.

    This is a forum post, but it gives a good description of what is going on in the blood itself:
    http://everything2.com/title/carbon+dioxide

    So CO2 is toxic because the hemoglobin needs to be able to hang on to both CO2 and O2 at the same time, but a small increase in CO2 concentration in the air makes the hemoglobin not get rid of CO2 fast enough. So while it can be said that the CO2 is displacing the O2 in your blood it isn't necessarily because it is displacing the O2 in the air because a small increase in ambient CO2 has a large effect on your blood's ability to get rid of it.
     
    Last edited: Apr 28, 2010
  13. Apr 28, 2010 #12

    mheslep

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    There are occasional deaths reported from young athletes who, as a stunt, breath pure O2 immediately before or after endurance sporting events. I suspect the cause goes something like this: body tissue gets saturated with O2, lungs 'believe' they can reduce activity accordingly, but then fall well below what is necessary to expel the rapid production of CO2 from the sporting event. The CO2 builds up rapidly causing acidosis which causes bleeding in the lungs and airway, victim drowns in their own blood.
     
  14. Apr 28, 2010 #13
    I think it's fair to say the situation is complicated. I find the explanation of inabiltiy to excrete carbon dioxide persuasive, but there seem to be contrary reports with both oxygen and carbon dioxide.

    I can't agree with the above statement. Otherwise there would be no point in oxygen treatment. But see my last comment, oxygen is sometimes poisonous.

    I took some time to look at your references.
    The inspectapedia one contradicted itself.
    The others were quite interesting, thank you.

    I also googled carbon dioxide poisoning as suggested and came up with some interesting controversy about several things including the mechanism.

    Googling carbon dioxide narcosis or carbon dioxide retention reveals significant controversy about the mechanism you suggest, although there is no doubt that at a local partial pressure equal to few percentage points of carbon dioxide, the body can have trouble excreting carbon dioxide and can suffer increasing symptoms up to and including death.

    Wikipedia for example does not exclude the alternative explanation, that I was taught in my diving training.

    http://en.wikipedia.org/wiki/CO₂_retention

    Googling oxygen poisoning also produces interesting results.
     
    Last edited: Apr 28, 2010
  15. Apr 28, 2010 #14

    Evo

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    Windows and doors are not airtight, so not too much of a worry.
     
  16. Apr 30, 2010 #15

    russ_watters

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    Yes. Here is a study/survey of infiltration rates in real houses: http://nepis.epa.gov/Exe/ZyNET.exe/...ckDesc=Results page&MaximumPages=1&ZyEntry=23

    Basically, it says if your house is in the best 5% of houses in the US, it'll have an infiltration rate of about .15 air changes per hour. For a 1500 square foot house with 8.5' ceilings (my townhouse), that's 31 cubic feet of air per minute. Humans breathe about 0.25 cubic feet of air per minute.
     
  17. Apr 30, 2010 #16

    Borek

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    Interesting. I always thought increased breathing speed is a response to the lowered pH level, not amount of oxygen in the blood. That means high level of carbon dioxide should immediately speed up breathing, as the blood pH goes down (bicarbonate buffer at action).

    I remember seeing movies of training that was done somewhere in sixties or even fifties with military pilots. They were put in an oxygen mask in a room filled with nitrogen, then they were asked to remove the mask and to perform some simple task (I think it was writing list of numbers, 1, 2, 3 and so on). They didn't start to breath rapidly, as they had no problem with carbon dioxide build up, and they were passing out not even knowing what is happening, as they run out of oxygen. Obviously their bodies were not aware of the problem.

    I think the idea was to help them learn early symptoms of the lack of oxygen, so that they can took countermeasures in high level flights, or something like that.
     
  18. Apr 30, 2010 #17
    Not anything scientific here, but many years ago I was calibrating the temperature controller on a smaller bench-sized temperature chamber. The cooling was done with CO2 from a large cylinder. I had just done a cold cycle, turned the unit on to heat, turned it off again immediately and removed the door that covered the entire front of the chamber. As I squatted down in front of the chamber to set the door on the floor under the bench I took a breath.
    I immediately jumped straight up, my heart pounding, and my entire body screaming at me, while my lungs fought to get some air. It was the most panic producing sensation I have ever experienced in my life.
    What had happened was, when I took the door off, the chamber full of CO2 had cascaded out over the edge of the bench and rolled down over my head just as I breathed in. I got a lung full of 100% CO2.
    As I came up I got a lung full of normal air and the effect was instantly gone. I just stood there with my heart pounding, realizing what had happened, laughing a little at my panic.

    If you want to torture someone, don't use water boarding, just spray a CO2 extinguisher into a bucket and with them secured down, dump it over their head. They will tell you anything you want to know.
     
  19. May 3, 2010 #18

    alxm

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    I don't have any references, but I'm almost certain I read that the real danger of a confined space is CO2 buildup (and not the classical "running out of air").
    Which is why CO2 scrubbers are so vital on submarines and spacecraft.
    They have plenty of bottled oxygen, it's the CO2 that's the problem.
     
  20. May 3, 2010 #19

    mgb_phys

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    The signal to breath is caused by the buildup of CO2 in your blood, so breathing a high concentration of CO2 fools this response into thinking that you really need another breath - however much O2 you still have. Your breath reflex is triggered by blood pH , CO2 makes your blood more acidic.

    There is a medical condition where this doesn't work and you rely on the level of Oxygen - so you give a victim of an accident pure oxygen and they stop breathing!
     
  21. May 3, 2010 #20

    Andy Resnick

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    I don't think that's correct- CO2 balance is related to pH control, since our bodies use bicarbonate as a buffer. At least, that's the role of CO2 in mammalian cell culture.

    IIRC, that's also why (chronically) breathing in too *high* a concentration of O2 is dangerous- it displaces the CO2, changing the pH levels.
     
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